Characterization and partial amino acid sequencing of a 107-kDa procollagen I N-proteinase purified by affinity chromatography on immobilized type XIV collagen.

Procollagen I N-proteinase (EC 3.4.24.14), the enzyme that specifically processes type I and type II procollagens to collagen, was isolated from extracts of fetal calf skin. After two chromatographic steps on concanavalin A-Sepharose and heparin-Sepharose, the semi-purified preparation was used to produce monoclonal antibodies. One reacting antibody was found to recognize not the enzyme itself but type XIV collagen on which the enzyme was bound. This binding, highly sensitive to ionic conditions (plH, salt concentrations) but not affected by non-ionic detergents, was used for affinity chromatography that strongly improved the purification procedure. The enzyme is extensively characterized: 1) it has a molecular mass of 107 kDa as determined by polyacrylamide gel electrophoresis in presence of SDS and of about 130 kDa when estimated by gel filtration on a Sephacryl-S300; 2) in standard assay (pH 7.5, 0.2 M NaCl, 35 degrees C), the activation energy for reaction with amino procollagen type I was 17,000 calories per mole. In the same conditions, Km and Vmax values were, respectively, 435 and 39 nM per hour but varied strongly with pH and salt concentration; 3) the enzyme cleaved the NH2-terminal propeptide of type I procollagen at the specific site, the Pro-Gln bond in the alpha 1 type I procollagen chain; 4) the enzyme contained a high proportion of Gly, Asx, and Glx residues but no Hyp or Hyl; 5) partial amino acid sequences obtained from internal peptides of the enzyme displayed no significant homology with known sequences. The association of procollagen I N-proteinase with a FACIT (fibril-associated collagens with interrupted triple helices) collagen as found here might be of physiological significance.

Procollagen type III N-terminal endopeptidase in fibroblast culture.

A peptidase activity capable of excising in a single fragment the N-terminal extension of the precursor of collagen type III (p-N-collagen type III) was observed in calf tendon fibroblast culture medium. A new procedure was developed for detecting this peptidase (p-N-collagen type III peptidase). It is based on the use of 14C-labelled p-N-collagen type III obtained by carboxymethylation of the half-cystine residues with iodo-[14C]acetamide. The released labelled N-terminal extension is soluble in 27% (v/v) ethanol, whereas the uncleaved substrate and the collagen are precipitated under these conditions. The endopeptidase nature of p-N-collagen type III peptidase is supported by the similarity in molecular weight of the product of cleavage of p-N-collagen III by the enzyme to those obtained by cleavage with bacterial collagenase. An apparent Km of 0.3 X 10(-6)M was established. The pH optimum of p-N-collagen type III peptidase is similar to that of p-N-collagen type I peptidase, i.e. about 7.5. Both peptidases are inhibited by dithiothreitol and by Cu2+ and Zn2+, but not by other bivalent ions. p-N-collagen type III peptidase does not cleave p-N-collagen I or p-N-gelatin I. Partial purification of p-N-collagen type III peptidase from fibroblast culture medium was performed by sieve chromatography on Ultrogel AcA-34 to yield two peaks of activity, of mol.wts. 170000 and 100000. Part of the activity was retained on affinity chromatography on concanavalin A--Sepharose. Studied as a function of the age of the culture, p-N-collagen type III peptidase activity produced by tendon fibroblasts parallels that of p-N-collagen type I peptidase and collagen synthesis.